Lymphoplasmacytic myeloma: an immunological, immunohistochemical and electron microscopic study.

An unusual case of a light chain plasma cell myeloma is described. The disease was initially characterized by a diffuse lymphoplasmacytic bone marrow involvement, but subsequently developed widespread extramedullary metastases with anaplastic tumors in the skin which histologically resembled a "histiocytic lymphoma." Electron microscopic examination, in vitro protein synthesis of bone marrow lymphoidal cells, chemical and immunochemical studies of serum and urine proteins, and intracellular immunoglobulin study by the immunoperoxidase technique on the skin biopsy and postmortem tumor tissue demonstrated evidence for lambda light chain synthesis and secretion. These findings provide further support to the notion that the wide spectrum of diverse morphologic patterns seen in lymphoplasmacytic disorders originates from the same progenitor B-lymphoid cell. Distinguishing anaplastic variant of plasma cell myeloma from other undifferentiated neoplasms offers a challenge.